It could, says Mark Walton, the hydrologist who keeps track of river conditions at the National Weather Service office in Grand Rapids.

But we probably would have two or three days of warning if the floodwalls that line the Grand River were threatened, Walton said Friday.

That is because it takes time for the Grand River's 5,000-square-mile watershed to drain and funnel through the city on its way to Lake Michigan.

For example, a drop of rain that falls into the headwaters of the Grand River near Jackson takes about five or six days to works its way down to Lake Michigan, Walton said.

The National Weather Service bases its forecasts on computer models that take into account rainfall, soil conditions and vegetation, Walton said.

In Grand Rapids, the floodwalls and embankments have been built at one foot above the theoretical 100-year-flood level. The city currently is in a dispute with the Federal Emergency Management Administration, which argues the walls should be set two feet higher.

Despite the recent heavy rains, the Grand River currently is below its flood stage, and its levels are expected to continue to fall, weather service officials said.

Walton said Grand Rapids' floodwalls could have been threatened as recently as 1986, when heavy rains fell in the neighboring Muskegon River watershed. More than a foot of rain fell in about 36 hours, threatening the Croton Dam and Hardy Dam in Newaygo County.

"That's kind of the scary thing," Walton said. "It could happen, and it has happened. It just hasn't happened over the Grand River Basin."

While the threat of flooding has not changed, the stakes are higher, Walton said. Increased urbanization has increased the damage caused by flooding and the risk of flooding.

For property owners worried about the threat, Walton recommends getting flood insurance. It is fairly affordable in low-risk areas and invaluable when disaster strikes, he said.

"The folks in Cedar Rapids, Iowa -- a lot of them never dreamed they'd need flood insurance. Now they're left holding the bag."